import java.util.*;

public class Main3 {
    public static void main(String[] args) {
        Scanner console = new Scanner(System.in);
        int m = console.nextInt();
        int n = console.nextInt();
        int result = getCM(m, n);
        System.out.println(result);
    }

    public static int getCM(int m, int n) {
        int max = (m > n) ? m : n;
        //write your code here......
        for (int i = max; i <= m*n; i++) {
            if (i % m == 0 && i % n == 0) {
                return i;
            }
        }return -1;
    }
}